The present invention relates to packages for food products and in particular to a microwavable package and an active microwave energy heating element for the same.
Microwave ovens have become a principle form of cooking food in a rapid and effective manner and the number of food products available for preparation in a microwave oven is constantly increasing. As the market for microwavable food products has increased, so the sophistication required from such food products has also increased. There is, therefore, a continuing demand to improve the quality of food prepared in a microwave oven and to ensure that when it is presented to the consumer, the food product is attractive and meets the standards normally associated with such food.
Foods that are specially prepared for cooking within a microwave oven are delivered to the consumer in containers that may be used directly within the microwave oven to facilitate preparation. These containers must therefore not only be capable of containing the food product during transport in an effective manner but must also be capable of contributing to the cooking of the food product within the microwave oven and the subsequent presentation of the food product.
As the demand for more sophisticated food products increases, so the demand for effects, particularly appearance, normally associated with food preparation also increases. For example, it is desirable for a food product that includes a pastry shell or lid to have a browned appearance, so that it appears to have been baked. While these effects can be produced in isolation, it becomes more difficult to produce such an effect in combination with a container that can also uniformly heat the food product within a time that offers advantages over conventional cooking techniques.
Typically, the areas in which browning or crisping are required are those on the outer surfaces of the food product. Those areas typically receive the highest proportion of incident microwave radiation and therefore cook or heat the quickest even though the power distribution is very non-uniform over these surfaces. On the other hand, there are areas of the food product that are relatively shielded from incident microwave radiation or exist in a region of a minimum RF field and which therefore require longer cooking periods. If, however, a longer cooking period is provided, the outer surfaces of the food product tend to char and burn, leading to an unacceptable food product.
Various attempts have been made in the past to provide containers that will produce effects normally associated with cooked foods. For example, U.S. Pat. No. 5,322,984 to Habeger, Jr. Et al. and assigned to The James River Corporation suggests a container having heating devices on the bottom wall and possibly the top wall of the container. The heating devices are designed to provide a charring effect normally associated with barbecuing by directing energy normally not incident upon the food product into specific regions. This is purported to produce a localised charring of the food product. Overall, however, such containers have not been successful. The charring effect produced on the food product may be attributed to the high field intensities and associated induced currents that result from the concentration of energy at particular locations. In practice it is found that those induced currents may also cause charring and burning of the container itself.
U.S. Pat. No. 4,927,991 to Wendt et al and assigned to The Pillsbury Company discloses a microwavable package for foodstuffs and in particular pizza. The package includes a tray on which a grid in combination with a susceptor are located. The grid and susceptor combination act together as a microwave energy heating element. The package also includes an aluminum top having apertures provided in it. The apertures allow microwave energy to penetrate the top thereby to heat the foodstuff.
It has also been found that in order to produce the required results for the preparation of the food product, the container must be capable of controlling distribution of energy about the food product, to utilize the energy in the most efficient manner, and at the same time ensure that the food product and the container provide a pleasant and acceptable finished product. Also, the containers must be able to hold the food product securely to avoid damage to the food product during transport. It has been found that in the case of pizza containers, conventional designs have not be adequate resulting in separation between the pizza crust and the toppings during transport.
It is therefore an object of the present invention to provide a novel food product package and active element for the same which obviates or mitigates at least one of the above disadvantages.
According to one aspect of the present invention there is provided a microwavable package comprising:
a base to support a food product;
an active microwave energy heating element on said base to effect heating of a food product upon impingement by microwave energy; and
a cover spaced from said active microwave energy heating element to overlie said food product, said cover including a microwave energy interactive material layer extending substantially over said food product, and a plurality of apertures in said microwave energy interactive material spaced about a peripheral margin of said cover, said apertures being sized to promote localized fields to promote browning of said food product.
In one embodiment, the apertures are in the form of elongate slots arranged in concentric rings. Microwave energy interactive material islands may be located within the slots to enhance further the cooking performance. In this embodiment, the active microwave energy heating element includes a plurality of energy collecting structures, each energy collecting structure having resonant loops. The resonant loops have a perimeter sufficient to limit currents induced therein to below a predetermined level upon impingement by incident microwave energy. The energy collecting structures distribute energy towards a central region of the food product to heat the food product generally uniformly and to inhibit charring of the base. In one form, the active microwave energy heating element further includes tuned structures at spaced locations each of which is located between a pair of the resonant loops.
According to another aspect of the present invention there is provided a microwavable packaging comprising:
a base to support a food product;
an active microwave energy heating element interposed between said food product and said base to effect heating of said food product upon impingement by microwave energy; and
a cover spaced from said active microwave energy heating element to overlie said food product, said cover including a substrate and microwave energy interactive material on said substrate to cover at least a portion of said food product, said substrate extending beyond the peripheral edge of said microwave energy interactive material to isolate electrically said base and said cover.
According to still yet another aspect of the present invention there is provided a packaged food product comprising:
a base to support said food product;
a flexible cover to overlie and conform to said food product; and
a flexible wrap to constrain said base and cover and inhibit relative movement therebetween.
According to still yet another aspect of the present invention there is provided an active microwave energy heating element for a microwavable package to heat generally uniformly a food product within said package, said active microwave energy heating element comprising:
a plurality of energy collecting structures, each of said energy collecting structures including resonant loops having a perimeter sufficient to limit currents induced therein to below a predetermined level upon impingement by incident microwave energy; and
a plurality of tuned structures at spaced locations and positioned between adjacent resonant loops, said energy collecting and tuned structures distributing energy across said active microwave energy heating element to heat generally uniformly said food product and inhibiting charring of said microwavable package.
In still yet another aspect of the present invention there is provided a microwavable package comprising:
a tray having a base and an active microwave energy heating element on said base to effect heating of a food product on said tray upon impingement by microwave energy; and
a plurality of spaced apertures in said tray to permit moisture released from a food product to pass through said tray.
The present invention provides advantages in that the microwavable package design is such to heat generally uniformly the food product while browning the outer periphery of the food product. This design is particularly suited to cooking pizzas.